Never went nostop to continental Europe or UK/Ireland on a narrow body, but I did BWI-KEF on a 757, 2762 miles. Trip was not to Iceland, though; I continued on to AMS (only another 1200-odd miles). Came back the same way. Although in Y on Icelandair, those flights were not nearly as bad as my SAN-ORD (1723 mi) on a jam-packed UA 757. Had an aisle seat but near the back of Y, and that seemed endless. I've also done LAX-ATL (1946 mi) on a DL 757. This was not as bad, near front in Y, aisle I think, and for once I slept quite a bit on the plane (was after NRT-LAX on the MD-11).